The present invention relates generally to the construction of catheters for angioplastic treatment of obstructed blood vessels, and more particularly to the construction and use of a novel catheter having a retractable blade at its distal end for forming incisions in atheromic plaque deposited within the blood vessels.
Balloon angioplasty was first described by Andreas Gruntzig in 1977. Dr. Gruntzig employed a balloon-tipped flexible catheter to percutaneously dilate a region of stenosis within the coronary artery of a patient with atherosclerotic coronary artery disease. Since the original work, the use of percutaneous balloon angioplasty has become widespread, with treatment of occluded peripheral blood vessels as well as coronary arteries.
Conventional balloon angioplasty relies on outward pressure from the balloon to compress the obstruction into the vessel wall. In successful treatment, the obstructing material remains compressed and unobstructed flow through the vessel is regained. In some cases, however, the atheromic material within the blood vessel has become hardened and calcified so that attempted dilation with a balloon causes cracking, tearing, and stretching of the blood vessel wall. In those cases, after the balloon catheter is removed, torn plaque and tissue can become dislodged from the vessel wall and cause abrupt reclosure of the vessel. Even when such abrupt reclosure does not occur, it appears that the irregular inner surface of the vessel wall (which results from the cracking and tearing) may contribute to restenosis at the same location within the vessel. In other cases, the plaque has so hardened that even with very high balloon pressures, successful dilation of the stenosed region is impossible.
For these reasons, it would be desirable to provide a method and apparatus for pretreating the region of stenosis to render the atheromic plaque more amenable to treatment by balloon angioplasty. It would be particularly desirable if such methods and apparatus greatly reduced or eliminated the incidence of restenosis after balloon dilation and allowed for successful balloon dilation in cases where the plaque would otherwise be refractory to such treatment.